Angle independent optical surface inspector

ABSTRACT

An angle independent optical surface inspector capable of generating a light beam, directing the light beam to a sample, and de-scanning a reflected light beam that is reflected from the sample, thereby generating a first de-scanned light beam. The de-scanning is performed at approximately one focal length of a de-scanning lens from an irradiation location where the light beam irradiates the sample. The optical inspector also capable of focusing the first de-scanned light beam, thereby generating a focused light beam, and measuring the location of the focused light beam. The measuring of the location is performed at approximately one focal length of a focusing lens from the focusing lens. The incident angle of the light beam is within ten degrees of Brewster&#39;s angle. The focusing is performed by an achromatic lens.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of, and claims priority under35 U.S.C. § 120 from nonprovisional U.S. patent application Ser. No.17/576,986, entitled “REGION PROBER OPTICAL INSPECTOR,” filed on Jan.16, 2022, the subject matter of which is incorporated herein byreference. In turn, nonprovisional U.S. patent application Ser. No.17/576,986 is a continuation-in-part of, and claims priority under 35U.S.C. § 120 from nonprovisional U.S. patent application Ser. No.16/838,026, entitled “REGION PROBER OPTICAL INSPECTOR,” filed on Apr. 2,2020, the subject matter of which is incorporated herein by reference.In turn, nonprovisional U.S. patent application Ser. No. 16/838,026 is acontinuation-in-part of, and claims priority under 35 U.S.C. § 120 fromnonprovisional U.S. patent application Ser. No. 16/289,632, entitled“PHASE RETARDANCE OPTICAL SCANNER,” filed on Feb. 28, 2019, the subjectmatter of which is incorporated herein by reference

TECHNICAL FIELD

The present invention generally relates to systems and methods fordetecting characteristics in materials. More specifically, the presentinvention relates to detecting characteristics in materials by way ofmeasuring light reflected from the materials.

BACKGROUND INFORMATION

Many thin films are used in high technology products. For example, thinfilms on glass are used in many high technology products such astelevisions, monitors, and mobile devices. Inspecting glass ischallenging due to its low reflectivity and high transparency. Previoustechniques perform glass inspection that requires the glass sample to bespun. Spinning a glass sample introduces problems for glass samples thatare fragile, not symmetric, or large. Regardless of these problems,glass samples that are fragile, not symmetric, or large need to betested for defects before used in costly manufacturing processes andintegrated into expensive high technology products.

SUMMARY

In a first novel aspect, an optical scanning system includes a radiatingsource capable of outputting a light beam, a first time varying beamreflector that is configured to reflect the light beam through a scanlens towards a transparent sample at an incident angle that is not morethan one degree greater or less than Brewster's angle of the transparentsample, and a second time varying beam reflector that is configured toreflect the light beam reflected from the transparent sample afterpassing through a de-scan lens onto a phase retardance detector. Theoutput of the phase retardance detector is usable to determine if adefect is present on the transparent sample. The first time varying beamreflector causes a first phase retardance of the light beam and thesecond time varying beam reflector causes a second phase retardance ofthe reflected light beam in the opposite direction of the first phaseretardance.

In one example, the optical scanning system further includes a memorycircuit and a processor circuit adapted to read information receivedfrom the phase retardance detector, and determine if a defect is presenton the transparent sample.

In a second novel aspect, an optical scanning system includes aradiating source capable of outputting a light beam, a time varying beamreflector that is configured to reflect the light beam through a scanlens towards a transparent sample at an incident angle that is not morethan one degree greater or less than Brewster's angle of the transparentsample, and a focusing lens configured to be irradiated by lightscattered from the transparent sample at an angle that is normal to theplane of incidence of the moving irradiated spot on the transparentsample. A first portion of the light beam is scattered from a firstsurface of the transparent sample and a second portion of the light beamis scattered from a second surface of the transparent sample. A spatialfilter is configured to block the second portion of the light beamscattered from the second surface of the transparent sample.

In one example, the optical scanning system further includes a memorycircuit and a processor circuit adapted to read information receivedfrom the detector and determine if a defect is present on the firstsurface of the transparent sample.

In a third novel aspect, the angle of incidence of the incident beam iswithin ten (10) degrees of Brewster's angle.

In a fourth novel aspect, an angle independent optical surface inspectorcapable of generating a light beam, directing the light beam to asample, and de-scanning a reflected light beam that is reflected fromthe sample, thereby generating a first de-scanned light beam. Thede-scanning is performed at approximately one focal length of ade-scanning lens from an irradiation location where the light beamirradiates the sample. The optical inspector also capable of focusingthe first de-scanned light beam, thereby generating a focused lightbeam, and measuring the location of the focused light beam. Themeasuring of the location is performed at approximately one focal lengthof a focusing lens from the focusing lens. The incident angle of thelight beam is within ten degrees of Brewster's angle. The focusing isperformed by an achromatic lens.

In a fifth novel aspect, an optical scanning system includes a radiatingsource capable of outputting a source light beam, a de-scan lens that isconfigured to output a de-scanned light beam, the de-scan lens islocated approximately one focal length of the de-scan lens from a sampleirradiation location, a focusing lens that is configured to output afocused light beam, a first non-polarizing beam splitter configured tobe irradiated by at least a portion of the focused light beam, a secondnon-polarizing beam splitter configured to be irradiated by at least aportion of the focused light beam that is reflected by the firstnon-polarizing beam splitter, and a detector that is located atapproximately one focal length of the focusing lens from the focusinglens, the detector is configured to be irradiated by at least a portionof the focused light beam that is reflected by the second non-polarizingbeam splitter.

In a sixth novel aspect, an optical scanning system includes a radiatingsource capable of outputting a source light beam, a de-scan lens that isconfigured to output a de-scanned light beam, the de-scan lens islocated approximately one focal length of the de-scan lens from ansample irradiation location, a focusing lens that is configured tooutput a focused light beam, a first non-polarizing beam splitterconfigured to be irradiated by at least a portion of the focused lightbeam, a second non-polarizing beam splitter configured to be irradiatedby at least a portion of the focused light beam that is reflected by thefirst non-polarizing beam splitter, and a detector that is located atapproximately one focal length of the focusing lens from the focusinglens, the detector is configured to be irradiated by at least a portionof the focused light beam that is not reflected by the secondnon-polarizing beam splitter.

In a seventh novel aspect, an optical scanning system including aradiating source capable of outputting a source light beam, a de-scanlens that is configured to output a de-scanned light beam, thede-scanned light beam is created by focusing light reflected from thesample and the de-scan lens is located approximately one focal length ofthe de-scan lens from an irradiation location where the light beamirradiates the sample, a focusing lens that is configured to output afocused light beam, a collimating lens that is configured to output acollimated light beam, a polarizing beam splitter that is configured tobe irradiated by the collimated light beam, and a detector that isconfigured to be irradiated by at least a portion of the collimatedlight beam that is not reflected by the polarizing beam splitter.

Further details and embodiments and techniques are described in thedetailed description below. This summary does not purport to define theinvention. The invention is defined by the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, where like numerals indicate like components,illustrate embodiments of the invention.

FIG. 1 is a cross-sectional diagram of a thin film deposited on top of aglass sample.

FIG. 2 is a graph illustrating the relationship between phase retardanceand the incident angle of irradiating light for a bare glass sample, a10 Å thin film deposited on a glass sample, and a 100 Å thin filmdeposited on a glass sample.

FIG. 3 is a diagram of a phase retardance optical inspector.

FIG. 4 is a diagram of a bi-cell detector.

FIG. 5 is a graph illustrating phase retardance caused by both the inputmirror and the output mirror when the mirrors are operating in anout-of-phase manner. More specifically, the graph illustrates therelationship between the phase of a beam reflecting off the input andoutput mirror versus the rotation angle of the input mirror.

FIG. 6 is a graph illustrating the combined phase retardance for bothin-phase mirror operation and out-of-phase mirror operation. Morespecifically, the graph illustrates the relationship between theresulting phase of the beam after being reflected by both the input andoutput mirrors versus the rotation angle of the input mirror.

FIG. 7 is a graph illustrating the relationship between total phaseretardance of the phase retardance optical inspector versus the field ofview of the phase retardance optical inspector at the location of thephase retardance detector.

FIG. 8 is a table listing an example of the angles of rotation for boththe input mirror and the output mirror when operated in an out-of-phasemanner.

FIG. 9 is a diagram of a beam retardance mapping illustrating thedetection of defects by way of detecting changes in the beam retardance.

FIG. 10 is a diagram of a scattered radiation optical inspector.

FIG. 11 is a diagram of a scattered radiation mapping illustratingdetection of defects by way of detecting changes in the intensity ofscattered radiation.

FIG. 12 is a flowchart illustrating the steps to perform phaseretardance defect detection.

FIG. 13 is a flowchart illustrating the steps to perform scatteredradiation defect detection.

FIG. 14 illustrates a novel region prober optical inspector.

FIG. 15 illustrates an example location to be probed on a transparentsample.

FIG. 16 illustrates the area of reflected light blocked by blocker 119from the perspective along the path of the reflected light.

FIG. 17 illustrates an example of a desired region of the transparentsample that is to be probed.

FIG. 18 is a table illustrating how the presence of a defect in a probedregion is detected using a threshold value.

FIG. 19 is a flowchart 300 illustrating the steps of region probing todetect defects within a desired region of a transparent sample.

FIG. 20 illustrates the two scattered radiation events caused by aninclusion.

FIG. 21 illustrates the two scattered radiation events caused by a topsurface particle.

FIG. 22 illustrates a scattered radiation event caused by a bottomsurface particle.

FIG. 23 is an example of separation ranges between scattered radiationevents for an exemplary transparent sample.

FIG. 24 is a flowchart 400 illustrating the steps to perform scatteredradiation defect depth detection.

FIG. 25 is a flowchart 500 illustrating the steps of defect detectionutilizing multiple measure polarization values.

FIG. 26 is a diagram of another phase retardance optical inspector.

FIG. 27 is a diagram of another scattered radiation optical inspector.

FIG. 28 is another flowchart illustrating the steps to perform phaseretardance defect detection.

FIG. 29 is another flowchart illustrating the steps to perform scatteredradiation defect detection.

FIG. 30 is a diagram of an angle independent surface height opticalinspector.

FIG. 31 is a diagram of a simplified example of angle independentsurface height optical inspector at different sample heights.

FIG. 32 is a diagram of a simplified example of an angle independentsurface height optical inspector at different sample angles.

FIG. 33 is a diagram of an electrical system for beam tracking positionsensitive detectors.

FIG. 34 is a flowchart of an angle independent surface height opticalinspector.

DETAILED DESCRIPTION

Reference will now be made in detail to background examples and someembodiments of the invention, examples of which are illustrated in theaccompanying drawings. In the description and claims below, relationalterms such as “top”, “down”, “upper”, “lower”, “top”, “bottom”, “left”and “right” may be used to describe relative orientations betweendifferent parts of a structure being described, and it is to beunderstood that the overall structure being described can actually beoriented in any way in three-dimensional space.

Many high technology products involve depositing films on glass or othertransparent substrates. An important process control metric is tomeasure the film thickness and film defects on the glass substrate. Thishas proven to be difficult due to the low reflectivity of glass and thedifficulty of separating signals from the top surface of the glasssubstrate from signals from the bottom surface of the glass substrate.Another issue with measuring the film thickness and film defects on theglass substrate is that the current techniques do not allow for scanningof many different shapes and sizes of transparent samples.

A solution is needed that: (i) accurately separates signals from the topsurface of the glass substrate from signals from the bottom surface ofthe glass substrate, (ii) detects the presence of defects in response tosmall changes in signals from the surface of the glass substrate, and(iii) allows for scanning of many different shapes and sizes oftransparent samples.

The present invention provides a solution to this problem by providing ascanning method that irradiates the transparent sample at, or near, theBrewster's angle of the transparent sample. This scanning method ofirradiating the transparent sample at, or near, Brewster's angle alsoprovides a scan in the x-y coordinate system, which makes the presentinvention capable of scanning any object shape or object size that issubstantially flat.

Transparent sample surfaces, such as glass, frequently have thin filmsdeposited upon their surfaces. FIG. 1 is a cross-sectional diagram of athin film deposited on top of a glass sample. It is desirable to be ableto inspect the transparent sample surface both before deposition forsurface cleanliness and after the deposition to check and for filmdefects. In order to achieve this goal, it is necessary that thetechnique be very sensitive to films on the transparent sample surface.It is also necessary that that the technique be able to separate thereceived signal from the top surface of the transparent sample from thereceived signal from the bottom surface of the transparent sample.

The sensitivity to films on a transparent sample can be addressed byconsidering the information illustrated in FIG. 2. FIG. 2 is a graphillustrating the relationship between phase retardance and the incidentangle of irradiating light for a bare glass sample, a 10 Å thin filmdeposited on a glass sample, and a 100 Å thin film deposited on a glasssample. More specifically, FIG. 2 shows the retardance (Φ_(P)−Φ_(S)+π)versus the angle of incidence for a typical transparent sample, such asglass (BK7) with a MgF₂ film layer thickness as a parameter. On a glasssubstrate, the retardance reduces to just the phase of the P wave(Φ_(P)). One conclusion to draw from FIG. 2 is that to detect films ontransparent samples, such as glass, it is desirable to operate with apolarization that is near P polarization (polarization that is parallelto the plane of incidence). Another conclusion to draw from FIG. 2 isthat it is desirable to perform the scan by irradiating the transparentsample at an incident angle that is at, or near, the Brewster's angle ofthe transparent sample. For example, ten times more (10×) sensitivitycan be achieved by operating at 57 degrees instead of at 60 degrees.Sensitivity is defined as the difference between the 10 Angstrom filmcurve and the bare glass curve. There is, however, a tradeoff given thatoperation at exactly Brewster's angle in P polarization will result inno signal being reflected from the transparent solid. Therefore, it isdesirable to perform the scan by irradiating the sample at an angle ofincidence that is no more than one degree greater or less thanBrewster's angle for the transparent sample. It is also desirable toperform the scan by irradiating the sample with a polarization that isno more than 20 degrees from P polarization.

FIG. 3 is a diagram of a phase retardance optical inspector. The phaseretardance optical inspector includes a radiating source 10, a half-waveplate 28, a feed-in mirror 11, an input mirror (input time varying beamreflector) 12, a scan lens 13, a de-scan lens 15, an output mirror(output time varying beam reflector) 16, a feed-out mirror 17, afocusing lens 18, a blocker 19 located at a focal plan 20 of thefocusing lens 18, a collimating lens 21, a half-wave plate 22, a phaseretardance measuring unit 29, a processor 26 (optional), and a memory 27(optional). The phase retardance measuring unit includes a polarizingbeam splitter 23, a first detector 24 and a second detector 25.

In one example, the input 12 and output 16 mirrors are linear timevarying beam reflectors, which vary the angle of reflection linearly asthey are rotated. Input 12 and output 16 mirrors may also be controlledby an electrical signal, such as a signal generator. Input 12 and output16 mirrors may be referred to as galvanometer mirrors.

In one example, the first and/or second detectors are bi-cell detectors.An example of a bi-cell detector is illustrated in FIG. 4. A bi-celldetector has a center line 31 that separates a first photo sensor from asecond photo sensor. The bi-cell detector can be configured so that itoutputs a first signal that indicates the difference between the lightintensity measured by one side of the detector and the light intensitymeasured by another side of the detector. The bi-cell detector also canbe configured so that it outputs a second signal that indicates thesummation of the light intensity measured by one side of the detectorand the light intensity measured by another side of the detector.

In operation, the phase retardance optical inspector measures retardanceby measuring the change in polarization of the signal from thetransparent sample that results from irradiation of the transparentsample by a scanning beam as it travels across a transparent sample. Inorder to accurately measure the change in polarization due to thesignals from the transparent solid, and not due to the phase retardancecaused by the inspector itself, it is required that the optics thatproduce the moving beam and the optics that de-scan and guide thesignals from the transparent solid produce minimal polarization change(retardance).

A major source of polarization change (retardance) caused by the phaseretardance optical inspector is the input 12 and output 16 mirrors. Thepolarization change (retardance) caused by input mirror 12 and outputmirror 16 is illustrated in FIG. 5. Input mirror 12 and output mirror 16can be operated in any desired manner based on their electric controlsignals, however, the manner in which the input 12 and output 16 mirrorsare operated has a large impact on the polarization change (retardance)introduced by the phase retardance optical inspector. The polarizationchange (retardance) produced by each mirror is a function of the angleof incidence of the light upon the mirror. The larger the angle ofincidence, the larger the polarization change (retardance).

In one example, the input mirror 12 and the output mirror 16 could beoperated such that the both mirrors operate in-phase, such that eachmirror is rotated so that each mirror has the same angle with respect tothe beam. This “In-Phase” operation of the input 12 and output 16mirrors causes maximum polarization change (retardance) because as theinput mirror 12 rotates to increase its angle with respect to the beamthe amount of polarization change caused by the input mirror increases,and as the output mirror 16 rotates to increase its angle with respectto the beam the amount of polarization change caused by the outputmirror increases. Therefore, the polarization change (retardance) causedby each mirror is always in the same direction and results in a maximumpolarization change. This maximum variation of phase change (retardance)during “In-Phase” operation is illustrated in FIG. 6. FIG. 6 clearlyshows that as the angle of mirror rotation increases, so does thepolarization change (retardance).

In another example, the input mirror 12 and the output mirror 16 couldbe operated such that the mirrors operate out-of-phase, such that eachmirror is rotated so that each mirror has the opposite angle withrespect to the beam. FIG. 8 is a table listing an example of the anglesof rotation for both the input mirror and the output mirror whenoperated in an out-of-phase manner. This “Out-of-Phase” operation of theinput 12 and output 16 mirrors causes minimum polarization change(retardance) because as the input mirror 12 rotates to increase itsangle with respect to the beam the amount of polarization change causedby the input mirror increases, and as the output mirror 16 rotates todecrease its angle with respect to the beam the amount of polarizationchange caused by the output mirror decreases. Therefore, thepolarization change (retardance) caused by each mirror is always in theopposite direction and resulting in a minimum. This minimum variation ofphase change (retardance) during “Out-of-Phase” operation is alsoillustrated in FIG. 6. FIG. 6 clearly shows that as the angle of mirrorrotation increases, polarization change (retardance) does not exceed twodegrees.

With respect to the Out-of-Phase operation, it is also noted that notonly is the polarization change (retardance) across the field of viewreduced by this technique, but also the reflectivity variation caused byeach mirror is reduced as well. This is because the reflectivity of theinput mirror is decreasing as its angle of incidence increases and theoutput mirror reflectivity is increasing since its angle of incidence isdecreasing. These two effects will nearly cancel one another resultingin a very minimal change in reflectivity versus angle of incidence.

Another major source of polarization change (retardance) caused by thephase retardance optical inspector is the feed-in angle of the scanningbeam upon the input mirror 12. As discussed above, the polarizationchange (retardance) is reduced as the angle of incidence approaches zerodegrees. However, from a practical point of view, feed-in angles ofapproximately five degrees are possible. In the phase retardance opticalinspector the feed-in angle is controlled by the configuration of theradiating source 10 and feed-in mirror 11. In one example, the radiatingsource 10 and feed-in mirror 11 are configured so that the resultingfeed-in angle to input mirror 12 is twelve degrees. A fixed feed-inangle of twelve degrees causes a minimal polarization change(retardance) by the input mirror 12.

In one example, the light reflected by the feed-in mirror irradiates theinput mirror 12 at an angle that is not greater than thirty degrees fromthe normal angle of the input mirror 12 (first time varying beamreflector) when the input mirror 12 is positioned at a mid-point of theinput mirror 12 rotational range.

Similarly, yet another major source of polarization change (retardance)caused by the phase retardance optical inspector is the feed-out angleof the signal from the transparent sample upon the output mirror 16. Asdiscussed above, the polarization change (retardance) is reduced as theangle of incidence approaches zero degrees. However, from a practicalpoint of view, feed-out angles of approximately five to fifteen degreesare possible. In the phase retardance optical inspector the feed-outangle is controlled by the configuration of the de-scanning lens 15,output mirror 16, and feed-out mirror 17. In one example, thede-scanning lens 15, output mirror 16, and feed-out mirror 17 areconfigured so that the resulting feed-out angle to output mirror 17 istwelve degrees. A fixed feed-out angle of twelve degrees causes aminimal polarization change (retardance) by the feed-out mirror 17.

The combination of the Out-of-Phase operation of the input 12 and output16 mirrors with the minimal feed-in and feed-out angles result in anoptical inspector that produces minimal polarization change(retardance). An example of the resulting polarization change(retardance) at the phase retardance measuring unit 29 versus field ofview of the optical inspector is illustrated in FIG. 7. This clearlyshows the advantage of out-of-phase mirroring versus in-phase mirroring.

The half-wave plate 28 can be used to adjust the polarization of thescanning beam output by the radiating source 10. In one example, thehalf-wave plate 28 is used to adjust the polarization of the scanningbeam to be as close as possible to P polarized. As discussed above, itis advantageous to scan a transparent sample with a near P polarizedscan beam.

The scan lens 13 operates to focus the scanning beam onto thetransparent sample. In one example, the scan lens 13 is a telecentricscan lens. Scan lens 13 is configurable such that the scanning beamoutput from the scan lens 13 irradiates the transparent sample at anangle that is not more than one degree from Brewster's angle of thetransparent sample. Another type of lens which may replace the scan lensis an achromat.

In one example, the transparent sample is glass. In another example, thetransparent sample is a thin film deposited on a transparent material.Other examples of transparent samples include but are not limited to:sapphire, fused silica, quartz, silicon carbide, and polycarbonate.

De-scan lens 15 operates to focus the signal from the transparent sampleonto output mirror 16. In one example, the de-scan lens 15 is anachromat. An achromat can be used for de-scanning because criticalfocusing and telecentricity is not needed when receiving the signal fromthe transparent sample. This is an economical benefit because anachromat is much less expensive than a telecentric lens. Other examplesof a de-scan lens include, but are not limited to: spherical singlet,spherical doublets, triplet, or aspheric lens.

Feed-out mirror 17 operates to reflect the signal from the output mirror16 to focusing lens 18. Focusing lens 18 has a focal plane 20. At thefocus of the focusing lens 18 there will be two spots (provided thesample is transparent) and these spots correspond to signal from the topand bottom surfaces of the sample. In one example, focusing lens 18 isan achromatic lens. Other examples of a focusing lens include but arenot limited to: spherical singlet, spherical doublets, triplet, oraspheric lens.

In one example, the light reflected by output mirror 16 irradiates thefeed-out mirror at an angle that is not greater than thirty degrees fromthe normal angle of output mirror 16 (the second time varying beamreflector) when output mirror 16 is positioned at a mid-point of outputmirror 16 rotational range.

Blocker 19 is located near the focal plane 20 and operates to block aportion of the signal from the transparent sample that is from aspecific surface of the transparent sample. For example, as illustratedin FIG. 3, blocker 19 may be configured so to block signal from thebottom surface of the transparent sample, while allowing the signal fromthe top surface of the transparent sample to pass. Although notillustrated, the blocker 19 can also be configured so to block signalfrom the top surface of the transparent sample, while allowing thesignal from the bottom surface of the transparent sample to pass. Inthis fashion, the phase retardance optical inspector is able todifferentiate signal from the top of the transparent sample from signalfrom the bottom of the transparent sample. In one example, the blocker19 is a mirror. Other examples of a blocker include but are not limitedto: an absorbing material, a blackened piece of aluminum, and a blackpainted piece of metal.

Collimating lens 21 operates to collimate the signal from thetransparent sample that is not blocked by blocker 19. In one example,the collimating lens 21 is an achromatic lens. Other examples of acollimating lens include but are not limited to: spherical singlet,spherical doublets, triplet, or aspheric lens.

Half-wave plate 22 operates to adjust the polarization of the signalfrom the transparent sample before irradiating polarizing beam splitter23 of the phase retardance measuring unit 29. In one example, thehalf-wave plate 22 adjusts the polarization of the signal from thetransparent sample so that the signals incident upon detectors 24 and 25are approximately equal.

Upon being irradiated, polarizing beam splitter 23 allows all lightpolarized in one direction to pass through to detector 25 and reflectsall light polarized in the other direction to detector 24. The plane ofthe polarizing beam splitter 23 is the same as the plane of the sample.Detector 24 outputs a signal indicating the intensity of the light thatirradiated detector 24. Detector 25 outputs a signal indicating theintensity of the light that irradiated detector 25. The differencebetween the signals from the two detectors is proportional to thepolarization change (retardance) of the scanning beam caused by defectsof the transparent sample or films on the transparent sample. Any smallchange in the film thickness or properties can be detected by comparingthe output signals of detectors 24, 25. The sum of the signals from thetwo detectors is proportional to the reflectivity of the transparentsample or films on the transparent sample.

In the case where the detectors are bi-cell detectors, the phaseretardance measuring unit can also determine a change in the surfaceslope of the transparent sample.

Processor 26 (optional) can be used to read the output signals fromdetectors 24 and 25. Processor 26 can execute code that calculates thedifference between the output signals and determine if a defect ispresent on the transparent sample as well as what type of defect thedefect is. The processor 26 may also store the intensity valuesindicated by the output signals in a memory 27 (optional). The processor26 may also read instructions from memory 27. The processor 26 may alsoread one or more threshold values to aid in the determination if adefect is present and the type of defect when a defect is present.

FIG. 9 is a diagram of a beam retardance mapping illustrating thedetection of defects by way of detecting changes in the beam retardance.This mapping can be created manually based on monitoring the output ofthe phase retardance measuring unit 29. Alternatively, this mapping canbe created automatically by a processor that samples the output of thephase retardance measuring unit 29 and stores the resulting differencecomputations in memory 27. The beam retardance mapping can then be usedto determine if a defect is present on the transparent sample or thethin film deposited on the transparent sample. For example, a decreasein the beam retardance can indicate a change in film thickness, a filmdefect or a particle defect on the transparent sample. Alternatively, anincrease in the beam retardance can indicate a change film thickness, afilm defect, or a particle defect on the transparent sample. This beamretardance mapping can also be output as a digital file that is sharablewith consumers of the transparent sample.

FIG. 10 is a diagram of a scattered radiation optical inspector. Thescattered radiation optical inspector includes a radiating source (notshown) that outputs a source beam 40, a time varying beam reflector 41,a telecentric scan lens 42, a focusing lens 46, a spatial filter 48, acollimating lens 49 and a detector 50.

In operation, the radiating source emits source beam 40 which irradiatestime varying beam reflector 41. The time varying beam reflector 41reflects the source beam 40 to the telecentric scan lens 42. The timevariance of the time varying beam reflector 41 causes a moving spot(scanning beam 43) to irradiate transparent sample 44. The time varyingbeam reflector 41 and the telecentric scan lens 42 are configured so toirradiate the transparent sample 44 with the scanning beam 43 at anangle of incidence that is not more than one degree from the Brewster'sangle of the transparent sample 44. The focusing lens 46 is configuredto be irradiated by scattered radiation from the transparent sample 44.The scattered radiation is radiated from the top surface of thetransparent sample 44, as well as from the bottom surface of thetransparent sample 44. The focusing lens 46 can be referred to as acollector of light. In one example, the focusing lens 46 is configuredto be oriented along an axis that is perpendicular to the planeincidence of scanning beam 43. In one example, the focusing lens 46 is alow F-number camera lens. The focusing lens 46 focuses light to a focalplane 47. The spatial filter 48 is located at focal plane 47 andoperates to filter out the scattered radiation from the bottom surfaceof the transparent sample 44, while allowing the scattered radiationfrom the top surface of the transparent sample 44 to pass through tocollimating lens 49. The collimating lens 49 is configured along an axisthat is perpendicular to the scanning beam 43. In one example, thespatial filter 48 is a slit shaped spatial filter to remove thescattered light from the bottom surface of the transparent sample 44. Inanother example, the collimating lens 49 is a pair of achromatic lensesthat shape the scattered radiation into a circular spot that irradiatesdetector 50. In yet another example, detector 50 is a photomultipliertube.

In another example, the scattered radiation optical inspector furtherincludes a processor and a memory. The processor functions to read theoutput signals generated by the detector 50 and store the lightintensity values indicated by the output signals in the memory. Theprocessor may also function to determine the presence of defects and thetype of defects. The processor may also function to generate a mappingof defects across the area of the transparent sample. The processor mayalso be configured to communicate the mapping of defects to anotherdevice or to a monitor.

The scattered radiation optical inspector described above gathersscattered radiation from the irradiated transparent sample 44 at anangle that is near perpendicular from the angle of incidence of thescanning beam 43. Moreover, the scattered radiation optical inspectorcan separate scattered radiation from the top surface of the transparentsample from scattered radiation from the bottom surface of thetransparent sample, which provides the valuable ability to detectdefects on a single side of a transparent sample.

The scattered radiation optical inspector can be integrated with thephase retardance optical inspector of FIG. 3 because both inspectorsrequire that the transparent sample be irradiated at an angle ofincidence that is not more than one degree from the Brewster's angle ofthe transparent sample.

FIG. 11 is a diagram of a scattered radiation mapping illustratingdetection of defects by way of detecting changes in the intensity ofscattered radiation from one surface of the transparent sample. Forexample, the scattered radiation mapping may show a location where thereis a decrease in measured intensity by detector 50. This decrease inmeasured intensity can be an indicator of a change in film thickness, afilm defect, or a particle defect. In another example, the scatteredradiation mapping may show a location where there is an increase inmeasured intensity by detector 50. This increase in measured intensitycan be an indicator of a change in film thickness, a film defect, or aparticle defect.

FIG. 12 is a flowchart 100 illustrating the steps to perform phaseretardance defect detection. In step 101, a transparent sample isirradiated at an angle of incidence that is not more than one degreegreater or less than the Brewster's angle of the transparent sample. Instep 102, an input mirror and an output mirror are rotated so that theinput mirror is at a minimum angle of incidence when the output mirroris at a maximum angle of incidence. In step 103, light reflected fromthe bottom surface of the sample is blocked. In step 104, the retardance(polarization change) of the light reflected from the top surface ismeasured. In step 105, it is determined if a defect is present at thescan location based on the measured retardance and one or more thresholdvalues.

FIG. 13 is a flowchart 200 illustrating the steps to perform scatteredradiation defect detection. In step 201, a transparent sample isirradiated at an angle of incidence that is not more than one degreegreater or less than the Brewster's angle of the transparent sample. Instep 202, the scattered radiation from the transparent sample is focusedusing a lens orientated at a normal angle to the plane of incidence ofthe moving irradiated spot on the sample. In step 203, the scatteredradiation from the bottom surface of the transparent sample is blocked.In step 204, the scattered radiation from the top surface of thetransparent sample is collimated. In step 205, the intensity of thescattered radiation from the top surface of the transparent sample ismeasured. In step 206, a determination is made as to whether a defect ispresent at the scan location based on the measured intensity and one ormore threshold values.

Region Prober Optical Inspector

FIG. 14 illustrates a novel region prober optical inspector. In oneembodiment, a region prober optical inspector includes a radiatingsource 110, a feed-in mirror 111, a linear time varying beam reflector112, a scan lens 113, a de-scan lens 115, a linear time varying beamreflector 116, a feed-out mirror 117, a focusing lens 118, a blocker 119that is located at the focusing lens focal plane 120, and a detector121. The region probing optical inspector may further include aprocessor 122 and memory 123 that are configured to process and store anintensity and/or phase output signal received from detector 121.

In one example, the input mirror 112 and output mirror 116 are lineartime varying beam reflectors, which vary the angle of reflectionlinearly as they are rotated. Input mirror 112 and output input mirror116 may also be controlled by an electrical signal, such as a signalgenerator. Input mirror 112 and output input mirror 116 may be referredto as galvanometer mirrors.

In one example, the detector is a bi-cell detector. An example of abi-cell detector is illustrated in FIG. 4. A bi-cell detector has acenter line 31 that separates a first photo sensor from a second photosensor. The bi-cell detector can be configured so that it outputs afirst signal that indicates the difference between the light intensitymeasured by one side of the detector and the light intensity measured byanother side of the detector. The bi-cell detector also can beconfigured so that it outputs a second signal that indicates thesummation of the light intensity measured by one side of the detectorand the light intensity measured by another side of the detector.

In operation, the radiating source 110 outputs a laser beam. In oneoptional embodiment, the phase of the output laser beam can be adjustedby a half wave plate that is located along the path of the output laserbeam. The output laser beam irradiates feed-in mirror 111 and isreflected toward input mirror 112 and then reflected to scan lens 113.Scan lens 113 operates to focus the scanning beam onto the transparentsample. In one example, the scan lens 113 is a telecentric scan lens.Scan lens 113 is configurable such that the scanning beam output fromthe scan lens 113 irradiates the transparent sample 114 at an angle thatis not more than one degree from Brewster's angle of the transparentsample 114. Another type of lens which may replace the scan lens is anachromat.

In one example, the transparent sample is glass. In another example, thetransparent sample is a thin film deposited on a transparent material.Other examples of transparent samples include but are not limited to:sapphire, fused silica, quartz, silicon carbide, and polycarbonate.

De-scan lens 115 operates to focus the signal from the transparentsample onto output mirror 116. In one example, the de-scan lens 115 atelecentric scan lens that is substantially identical to scan lens 113.De-scan lens 115 can be a telecentric lens or an achromat lens.Utilization of substantially identical lens for scan lens 113 andde-scan lens 115 allows the system to focus on light reflecting from avery thin cross section region of the transparent sample. Other examplesof a de-scan lens include, but are not limited to: spherical singlet,spherical doublets, triplet, or aspheric lens.

Feed-out mirror 117 operates to reflect the signal from the outputmirror 116 to focusing lens 118. Focusing lens 118 has a focal plane120. At the focus of the focusing lens 118 there will be two spots(provided the sample is transparent and no defects are present) andthese spots correspond to signals from the top and bottom surfaces ofthe sample. In one example, focusing lens 118 is an achromatic lens.Other examples of a focusing lens include but are not limited to:spherical singlet, spherical doublets, triplet, or aspheric lens.

In one example, the light reflected by output mirror 116 irradiates thefeed-out mirror at an angle that is not greater than thirty degrees fromthe normal angle of output mirror 116 (the second time varying beamreflector) when output mirror 116 is positioned at a mid-point of outputmirror 116 rotational range.

Blocker 119 is located near the focal plane 120 and operates to blockall but a portion of the signal from the transparent sample that iswithin the desired region of the transparent sample. For example, asillustrated in FIG. 14, blocker 119 may be configured so as to blocksignal from the bottom surface of the transparent sample and the topsurface of the transparent sample, while allowing the signal from adesired region of the transparent sample to pass. An expandedillustration of one embodiment of blocker 119 is shown in FIG. 14. Theexpanded illustration shows the blocker as a slit with a center openingthat allows light to pass while blocking the remainder of blocked light.It is noted herein that other blocker configurations can be used toachieve the desired blocking. FIG. 15 illustrates an example location tobe probed on a transparent sample.

FIG. 17 illustrates an example of a desired region of the transparentsample that is to be probed. Examination of FIG. 17 shows that thedesired region to be probed within the transparent sample does notinclude the top surface or the bottom surface of the transparent solid.Rather, the desired region to be probed only includes a narrow interiorregion of the transparent sample. It is noted that the desired probingregion illustrated in FIG. 17 is exemplary and in operation any regionup to and including the top and bottom surfaces of the transparentsample may be part of the desired probing region.

FIG. 16 illustrates the area of reflected light blocked by blocker 119from the perspective along the path of the reflected light. The locationof the light reflected from different regions of the transparent samplevary from the center point (top surface reflection) along a line thatterminates at the location where bottom surface location is present. Theselectable portion of reflected light illustrated in FIG. 16 iscontrolled by blocker 119 as described above. Accordingly, adjusting theslit width of blocker 119 and the location of blocker 119 will adjustthe height and location of the region of the transparent sample thatwill travel past blocker 119 and be subsequently probed for defectdetection.

In this fashion, the region probing optical inspector is able todifferentiate reflections originating from the desired region of thetransparent sample from reflections originated from outside of thedesired region of the transparent sample. In one example, the blocker119 is a mirror. Other examples of blocker materials include but are notlimited to: an absorbing material, a blackened piece of aluminum, and ablack painted piece of metal.

An optional collimating lens (not shown) may be used to collimate thesignal from the transparent sample that is not blocked by blocker 119.In one example, the collimating lens is an achromatic lens. Otherexamples of a collimating lens include but are not limited to: sphericalsinglet, spherical doublets, triplet, or aspheric lens.

The unblocked light reflected from the desired region of the transparentsample then irradiates the detector 121. In response to beingirradiated, detector 121 outputs a signal that is proportional to theintensity of light that irradiates detector 121. The output signal isthen processed by processor 122 to determine if a defect is present inthe desired region of the transparent sample 114.

FIG. 18 illustrates the use of threshold values to determine if a defectis present in the desired region of the transparent sample. The measuredintensity of the reflected light from the desired region of thetransparent sample that passes the blocker 119 is compared with athreshold value. In one example, when the measured intensity is greaterthan the threshold value, it is determined that a defect is present inthe desired probing region. Alternatively, when the measured intensityis less than or equal to the threshold value, it is determined that adefect is not present in the desired probing region.

It also noted herein, that the phase retardance optical inspectorillustrated in FIG. 3 may also be utilized to implement a region proberoptical inspector. As described above regarding FIG. 3, the phaseretardance optical inspector can be used to measure changes in phase ofthe measured reflected light from the transparent sample. Using theblocker 119 as described regarding FIG. 14 and the phase retardancemeasuring unit of FIG. 3 in combination allows for the detection ofdefects by analyzing changes in the phase of the reflected light insteadof changes in the intensity of the reflected light. In this scenario,the polarization of the reflected light that passed blocker 119 can becompared to one or more threshold values to determine if a defect ispresent in the desired probing region.

FIG. 19 is a flowchart 300 illustrating the steps of region probing todetect defects within a desired region of a transparent sample. In step301, the transparent sample is irradiated at an angle of incidence thatis between zero and ninety degrees of the surface of the transparentsample. In step 302, reflected radiation from the transparent sample isfocused at a focal plan using a scan lens and a de-scan lens. In step303, one or more portions of the reflected radiation are blocked at thefocal plan using a blocker. In step 304, the intensity of the reflectedradiation that is not blocked by the blocker is measured. In step 305,the presence of a defect in a region of the transparent sample where theunblocked portion of the reflected light was reflected from isdetermined based at least in part on the measured intensity and one ormore threshold values.

Defect Detection Utilizing Multiple Measured Polarization Values

In addition to determining that a defect is present in desired probingregion by comparing a single intensity or a single-phase measurementwith a set threshold value, the presence of a defect can be determinedby comparing a single measurement with a group of other measurementvalues taken from the same sample. The optical inspector of FIG. 3 canbe used as described above at multiple locations on the transparentsample. The group of measurements taken at the multiple locations canthen be post processed to determine if a defect is present at eachmeasured location on the transparent sample.

In one example, the presence of a defect at first location on the sampleis determined by comparing the single measured polarization at the firstlocation with an average of measured polarization values within apredefined distance from the first location on the sample. In thisfashion, all the measured polarization values with the predefineddistance from the first location and summed and divided by the count ofqualifying measurements. The resulting average polarization value forthe group is then compared to the single polarization measurement takenat the first location.

In a first embodiment, if the measured phase value is greater or lessthan the average polarization value of the group plus or minus somethreshold, then it is determined that a defect is present at the firstlocation. If the measured phase value is less than or equal to theaverage polarization value of the group plus or minus some threshold,then it is determined that a defect is not present at the firstlocation. Depending upon the nature of the defect, a measured phasevalue which is greater or less than the average value plus or minus athreshold can be considered a defect.

In a second embodiment, if the measured phase value is greater than theaverage polarization value of the group by more than a threshold value,then it is determined that a defect is present at the first location. Ifthe measured phase value is less than the average polarization value ofthe group by more than a threshold value, then it is determined that adefect is not present at the first location.

In another example, the presence of a defect at first location on thesample is determined by comparing the single measured polarization atthe first location with a median of measured polarization values withina predefined distance from the first location on the sample. In thisfashion, all the measured polarization values with the predefineddistance from the first location are sorted and then counted. The valueat the position of the total count divided by two is selected as themedian value. The resulting median polarization value for the group isthen compared to the single polarization measurement taken at the firstlocation.

In a first embodiment, if the measured phase value is greater than themedian polarization value of the group by more than a threshold value,then it is determined that a defect is present at the first location. Ifthe measured phase value is less than or equal to the medianpolarization value of the group by more than a threshold value, then itis determined that a defect is not present at the first location.

FIG. 25 is a flowchart 500 illustrating the steps of defect detectionutilizing multiple measured polarization values. In step 501, the sampleis scanned using the region probing optical inspector to measurepolarization values across the sample. In step 502, a processing filteris applied to the raw measured data. This step is optional. In step 503,a group polarization value (average or median) of a group ofpolarization measurements is determined. In step 504, the grouppolarization value is compared with a single measured polarizationvalue. In step 505, presence of a defect at the location where thesingle measured polarization was measured is determined based on theresult of the comparison of the group polarization value and the singlemeasured polarization value.

Scattered Radiation Defect Depth Detection

As described above, using the scattered radiation optical detector ofFIG. 10, defects can be detected by analyzing a single scatteredradiation measurement. However, the scattered radiation optical detectorof FIG. 10 can be used in a new and novel way to detect defects byanalyzing the distance between multiple scattered radiation events. Thisnew and novel use of the scattered radiation optical detector of FIG. 10also removes the requirement that the scanning beam be oriented at anincident angle that is not more than one degree greater or less thanBrewster's angle of the transparent sample. Rather, the new and noveluse of the scattered radiation optical detector of FIG. 10 allows thescanning beam to be oriented at any incident angle.

This new and novel use of the scattered radiation optical detector ofFIG. 10 can determine the x, y and z location of a defect by analyzingthe distance between multiple scattered radiation events. A scatteredradiation event is when the intensity of the measured scatteredradiation is greater than a threshold intensity value.

A first example of defect depth detection is illustrated in FIG. 20. Aninclusion (defect) 251 is located at a depth d within the transparentsample 250. At time t1, the incident beam radiates the transparentsample 250 at an incident angle of ∅ degrees from normal. Due to thetransparent sample's index of refraction n, the light is redirected to adifferent angle as it travels from the top surface of the transparentsample to the bottom surface of the transparent sample. When the lightreaches the bottom surface of the transparent sample, light is reflectedupwards at an equal but opposing angle. The light travels at this equaland opposing angle until the reflected light reaches the top surface ofthe transparent sample, where the reflected light is redirected to anangle equal and opposite to the incident angle. Given that the path thelight travels through the transparent sample is known, then the presenceand the depth of a defect can be detected by analyzing multiplescattered radiation events measured along a single axis.

The following equation is the relationship between the thickness of thetransparent sample (t), separation between scattered radiation events(x), the index of refraction of the transparent sample (n), the angle ofincidence of the scanning beam (∅), and the depth of the defect (d).

$d = {t - \frac{x\sqrt{n^{2} - {sin^{2}\phi}}}{2\mspace{11mu}\sin\;\phi}}$

This equation is correct as long as the separation between scatteredradiation events is within a specific range.

When the separation between scattered radiation events is greater than afirst threshold, it is determined that the defect or particle is locatedat the bottom surface of the transparent sample.

FIG. 21 illustrates the two scattered radiation events caused by a topsurface particle. At time t1, the incident beam enters the transparentsample, reflects from the bottom surface of the transparent sample andirradiates the top surface particle as the beam exits the top surface ofthe transparent sample. This causes a first scattered radiation event attime t1. At time t2, the incident beam irradiates the top surfaceparticle before the beam has a chance to enter the transparent sample.This causes a second scattered radiation event. These two scatteredradiation events caused by a top surface particle will always be thesame distance apart for a given transparent wafer with a constantthickness and index of refraction. Therefore, any separations betweenscattered radiation events that are greater than, or less than, thisfixed distance are not top surface particles. The other criterion placeupon the two scattering events is that they must be directly above oneanother, namely they must have the same x coordinate (within a specifiedtolerance).

FIG. 20 illustrates the two scattered radiation events caused by aninclusion (defect within the transparent sample). At time t1, theincident beam enters the transparent sample, reflects from the bottomsurface of the transparent sample and irradiates the inclusion as thebeam travels toward the top surface of the transparent sample. Thiscauses a first scattered radiation event at time t1. At time t2, theincident beam enters the transparent sample and then irradiates theinclusion. This causes a second scattered radiation event. These twoscattered radiation events caused by the inclusion will always be thecloser together than the separation of the two scattered radiationevents caused by a top surface particle. Therefore, any separationsbetween scattered radiation events caused by a single inclusion (defectswithin the transparent sample) will never have a greater separation thanscattered radiation events caused by a top surface particle. The othercriterion place upon the two scattering events is that they must bedirectly above one another, namely they must have the same x coordinate(within a specified tolerance).

Accordingly, and two scattered radiation events that have a separationgreater than the fixed separation (and have the same x coordinate)between scattered radiation events caused by a top surface particle arenot caused by a top surface particle and are not caused by an inclusionparticle. Thus, by process of elimination, the two scattered radiationevents that have a separation greater than the fixed separation betweenscattered radiation events caused by a top surface particle must be theresult of a bottom surface particle.

When the separation between scattered radiation events is less than thefirst threshold and greater than a second threshold, it is determinedthat the defect or particle is located at the top surface of thetransparent sample. The reasoning of this second threshold isillustrated in FIG. 21. As discussed above, the two scattered radiationevents caused by a top surface particle will always be the same distanceapart for a given transparent wafer with a constant thickness and indexof refraction. Therefore, as shown in FIG. 23, the separation range fortop surface particles is relatively narrow because all top surfaceparticles should cause two scattered radiation events at substantiallysimilar distances. In practice, a narrow range is used to identify a topsurface particle due to measurement precision and potential variationsof particle size and shape. The other criterion place upon the twoscattering events is that they must be directly above one another,namely they must have the same x coordinate (within a specifiedtolerance).

When the separation between scattered radiation events is less than thesecond threshold and greater than a third threshold, it is determinedthat the defect or particle is an inclusion defect located within thetransparent sample (not a surface defect or particle) and the aboveequation is applicable to determine the depth of the defect in thetransparent sample. As discussed above regarding FIG. 20, anyseparations between scattered radiation events caused by a singleinclusion (defects within the transparent sample) will never have agreater separation than scattered radiation events caused by a topsurface particle. Therefore, any substantial separation betweenscattered radiation events that is less than the fixed separationbetween scattered radiation events caused by top surface particles mustbe an inclusion.

When the separation between scattered radiation events is less than thethird threshold, it is determined that the defect or particle is locatedat the bottom surface of the transparent sample. The reasoning for thisfirst threshold is illustrated in FIG. 22. FIG. 22 illustrates that abottom surface particle is only irradiated by the incident beam at timet1. Therefore, theoretically there should only be a single scatteredradiation event for bottom surface particles. However, due tomeasurement accuracy and variation of bottom surface particles size andshape, a practical range of very closely separate scattered radiationevents are determined to be cause by a bottom surface particle.

FIG. 23 is an example of separation ranges between scattered radiationevents for a five-hundred-micron thick transparent sample with a scanbeam incident angle of 56.3° and an index of refraction of 1.5. When theseparation between scattered radiation events is greater than a firstthreshold of six-hundred and eighty-six microns, it is determined thatthe defect or particle is located at the bottom surface of thetransparent sample and the above equation is not applicable. When theseparation between scattered radiation events is less than the firstthreshold of six-hundred and eighty-six microns and greater than asecond threshold of six-hundred and forty-six microns, it is determinedthat the defect or particle is located at the top surface of thetransparent sample. When the separation between scattered radiationevents is less than the second threshold of six-hundred and forty-sixmicrons and greater than a third threshold of twenty microns, it isdetermined that the defect or particle is an inclusion defect locatedwithin the transparent sample (not a surface defect or particle) and theabove equation is applicable to determine the depth of the defect in thetransparent sample. The other criterion place upon the two scatteringevents is that they must be directly above one another, namely they musthave the same x coordinate (within a specified tolerance). When theseparation between the scattered radiation events is less than the thirdthreshold of twenty microns, it is determined that the defect orparticle is located on the bottom surface of the transparent sample.

FIG. 24 is a flowchart 400 illustrating the steps to perform scatteredradiation defect depth detection. In step 401, the transparent sample isirradiated. In step 402, scattered radiation from the transparent sampleis focused using a lens. In step 403, the intensity of the scatteredradiation from the transparent sample is measured along a single axis.In step 404, the locations of increase scattered radiation along thesingle axis are determined. In step 405, the presence of a defect andthe depth of the defect are determined using the distance between thelocations of increased scattered radiation along the single axis

FIG. 26 is a diagram of another phase retardance optical inspector.Additional testing and research has indicated that the phase retardanceoptical inspector described above works well up to plus or minus ten(10) degrees from Brewster's angle (not only plus or minus 1 degree asdisclosed in the parent application). The performance varies as thedistance from Brewster's angle varies. For example, if the deviceoperates at an incidence angle of 56.8 degrees (0.1 degrees fromBrewster's angle) the difference between the 100 Angstroms of MgF2 andthe bare substrate is about 70 degrees of retardance. Whereas if thedevice operates at an incidence angle of 60 degrees the differencebetween the 100 Angstroms of MgF2 and the bare substrate is about 10degrees of retardance. So you give up a factor of seven times insensitivity but the inspector still works even though you are operatingat an angle which is 3.3 degrees away from the Brewster's angle of thesubstrate.

FIG. 27 is a diagram of another scattered radiation optical inspectordepicting an incident angle that is plus or minus ten (10) degrees ofBrewster's angle.

FIG. 28 is another flowchart illustrating the steps to perform phaseretardance defect detection using an incident angle that is plus orminus ten (10) degrees of Brewster's angle.

FIG. 29 is another flowchart illustrating the steps to perform scatteredradiation defect detection using an incident angle that is plus or minusten (10) degrees of Brewster's angle.

FIG. 30 is a diagram of an angle independent surface height opticalinspector. In one embodiment, an angle independent surface heightoptical inspector includes a radiating source 510, a feed-in mirror 511,a linear time varying beam reflector 512, a scan lens 513, a de-scanlens 515, a linear time varying beam reflector 516, a feed-out mirror517, a focusing lens 518, a non-polarizing beam splitter 519, acollimating lens 523, a half-wave plate 524, a polarizing beam splitter525, a detector 526, a detector 527, a non-polarizing beam splitter 520,a detector 521, a detector 522, a processor 528 and a memory 529.Optionally, the angle independent surface height optical inspector mayalso include a half-wave plate 526.

The de-scan lens 515 is located at approximately one focal length ofde-scan lens 515 from the sample 514. Similarly, the linear time varyingbeam reflector 516 is located approximately one focal length of thede-scan lens 515 from the de-scan lens 515.

The processor 528 and memory 529 that are configured to process andstore an intensity, irradiation location and/or phase output signalreceived from detector 521, detector 522, detector 526 and detector 527.

In one example, the input mirror 512 and output mirror 516 are lineartime varying beam reflectors, which vary the angle of reflectionlinearly as they are rotated. Input mirror 512 and output input mirror516 may also be controlled by an electrical signal, such as a signalgenerator. Input mirror 512 and output input mirror 516 may be referredto as galvanometer mirrors.

In one example, the detectors 521, 522, 526 and 527 are any combinationof bi-cell detectors, quad-cell detectors and/or position sensitivedetectors. An example of a bi-cell detector is illustrated in FIG. 4. Abi-cell detector has a center line 31 that separates a first photosensor from a second photo sensor. The bi-cell detector can beconfigured so that it outputs a first signal that indicates thedifference between the light intensity measured by one side of thedetector and the light intensity measured by another side of thedetector. The bi-cell detector also can be configured so that it outputsa second signal that indicates the summation of the light intensitymeasured by one side of the detector and the light intensity measured byanother side of the detector. A quad-cell detector includes four photosensors. Usually, the four sensors are evenly sized and are separated bya center vertical line and a center horizontal line. The quad-celldetector can be configured so that it outputs a signal that indicatesthe difference between the light intensity measured by each photosensor. The quad-cell detector also can be configured so that it outputsa second signal that indicates the summation of the light intensitymeasured by each photo detector. A position sensitive detector is aphoto detector that can measure the position of a light spot in one ortwo dimensions, normally with a relatively high speed. The positionsensitive detector can be configured so that it outputs a first signalthat indicates the position on the detector that is irradiated. Theposition sensitive detector can also be configured to output a secondsignal that indicates the intensity of the light that irradiates thedetector.

In operation, the radiating source 510 outputs a laser beam. In oneoptional embodiment, the phase of the output laser beam can be adjustedby a half wave plate that is located along the path of the output laserbeam. The output laser beam irradiates feed-in mirror 511 and isreflected toward input mirror 512 and then reflected to scan lens 513.Scan lens 513 operates to focus the scanning beam onto the transparentsample. In one example, the scan lens 513 is a telecentric scan lens.Scan lens 513 is configurable such that the scanning beam output fromthe scan lens 513 irradiates the transparent sample 514 at an angle thatis not more than ten (10) degrees from Brewster's angle of the sample514. Another type of lens which may replace the scan lens is anachromat.

In one example, the sample 514 is opaque. In another example, the sample514 is semi-transparent. In yet another example, the sample 514 istransparent. For example, the transparent sample 514 may be glass, athin film deposited on a transparent material, sapphire, fused silica,quartz, silicon carbide, and polycarbonate.

De-scan lens 515 operates to focus the signal from the sample 514 ontooutput mirror 516. In one example, the de-scan lens 515 a telecentricscan lens that is substantially identical to scan lens 513. De-scan lens515 can be a telecentric lens or an achromat lens. Utilization ofsubstantially identical lens for scan lens 513 and de-scan lens 515allows the system to focus on light reflecting from a very thin crosssection region of the transparent sample. For example, two telecentricscan lenses may have a field of view greater than one-hundred (100)millimeters. Other examples of a de-scan lens include, but are notlimited to: spherical singlet, spherical doublets, triplet, or asphericlens.

Feed-out mirror 517 operates to reflect the signal from the outputmirror 516 to focusing lens 518. Focusing lens 518 has a focal distancebased on the focusing lens characteristics. At the focus of the focusinglens 518 there will be two spots (provided the sample is transparent andno defects are present) and these spots correspond to signals from thetop and bottom surfaces of the sample. In the event that the sample isnot transparent, there will be a single spot from the top surface of thesample. In one example, focusing lens 518 is an achromatic lens with afour-hundred (400) millimeter focal length. Other examples of a focusinglens include but are not limited to: spherical singlet, sphericaldoublets, triplet, or aspheric lens.

In one example, the light reflected by output mirror 516 irradiates thefeed-out mirror at an angle that is not greater than thirty degrees fromthe normal angle of output mirror 516 (the second time varying beamreflector) when output mirror 516 is positioned at a mid-point of outputmirror 516 rotational range.

Non-polarizing beam splitter 519 irradiated by the light focused byfocusing lens 518. Upon being irradiated, non-polarizing beam splitter519 allows a specified portion of the light intensity to pass through tocollimating lens 523 and the remaining portion to be reflected tonon-polarizing beam splitter 520. The polarization of the transmittedand reflected beams from non-polarizing beam splitter 519 are unchanged.The planes of the non-polarizing beam splitters 519 and 520 can be thesame as or perpendicular to the plane of the sample. Upon beingirradiated, non-polarized beam splitter 520 allows a specified portionof the light intensity to pass through to detector 521 and reflects theremaining intensity in the other direction to detector 522. Thepolarization of the transmitted and reflected beams from non-polarizedbeam splitter 520 are unchanged. Detector 521 and detector 522 arelocated approximately one focal length of focusing lens 518 fromfocusing lens 518.

Detector 521 is configured to track the focus of the light beam.Detector 521 has a low bandwidth of approximately 20 kHz. Detector 521provides feedback to a sample height control system which maintains thesample at precisely the correct focus. An example of a sample heightcontrol system is illustrated in FIG. 33 and described in theaccompanying description below.

Detector 522 is a configured to measure the micro-surface profile of thesample. Detector 522 has larger bandwidth of approximately 2 MHz. Theoutput signal from detector 522 is used to measure sub-micron heightchanges on the sample.

Collimating lens 523 is configured to redirect the focused light beamfrom focusing lens 518 to a collimated (i.e., parallel) light beam. Thecollimated light beam irradiates half wave plate 524. Half wave plate524 rotates the plane of polarization of the collimated light beam. Therotated collimated light beam then irradiates polarizing beam splitter525. Upon being irradiated, polarizing beam splitter 525 allows alllight polarized in one direction to pass through to detector 527 andreflects all light polarized in the other direction to detector 526. Theplane of the polarizing beam splitter 525 is the same as the plane ofthe sample.

Detector 526 is configured to measure the s-component of the polarizedlight beam. Detector 526 may be a bi-cell, quad-cell, position sensitivedetector, PIN diode (single element) or other type of Si based detector.

Detector 527 is a configured to measure the sample surface slope and thep-component of the polarized light beam. Detector 527 may be a bi-cell,quad-cell, position sensitive detector, PIN diode (single element) orother type of Si based detector.

FIG. 31 is a diagram of a simplified example of an angle independentsurface height optical inspector at different sample heights. In a firstscenario, the sample 600 is located a height “A”, it is irradiated withan irradiating beam. The irradiating beam is reflected from the topsurface of the sample 600 thereby generating height “A” reflection thatirradiates a de-scan lens 601 on center. The de-scan lens 601 is locatedat one de-scan lens focal length from the irradiation point on thesample 600. The de-scan lens 601 then directs the height “A” reflectionto focusing lens 602 on center. Focusing lens 602 then directs theheight “A” reflection to a point centered on the detector 603. In asecond scenario, the sample is located at a height “B”, it is irradiatedwith an irradiating beam. Given that the height “B” is lower than height“A”, a different point on the surface of the sample is irradiated by thestationary irradiating beam. The irradiating beam is reflected from thetop surface of the sample 600 thereby generating height “B” reflectionthat is directed to a position off center on a de-scan lens 601. Thede-scan lens 601 is located at one de-scan lens focal length from theirradiation point on the sample 600. The de-scan lens 601 then directsthe height “B” reflection to focusing lens 602. Since the height “B”reflection irradiates the de-scan lens 601 off center, the height “B”reflection emitted by de-scan lens 601 is not parallel to the height “A”reflection and irradiates focusing lens 602 off center as well. Focusinglens 602 then directs the height “B” reflection to a point that is notcentered on the detector 603. The distance between the point ofirradiation of height “A” reflection on the detector and the point ofirradiation of height “B” on the detector is proportional to the changein height of the sample between the two measurements.

FIG. 32 is a diagram of a simplified example of an angle independentsurface height optical inspector at different sample angles. In a firstscenario, the sample 610 is located an angle “A”, it is irradiated withan irradiating beam. The irradiating beam is reflected from the topsurface of the sample 610 thereby generating angle “A” reflection thatirradiates a de-scan lens 611 on center. The de-scan lens 611 is locatedat one de-scan lens focal length from the irradiation point on thesample 610. The de-scan lens 611 then directs the angle “A” reflectionto focusing lens 612 on center. Focusing lens 612 then directs the angle“A” reflection to a point centered on the detector 613. In a secondscenario, the sample is located at an angle “B”, it is irradiated withan irradiating beam. Given that the angle “B” is different than angle“A”, the same point on the surface of the sample is irradiated by thestationary irradiating beam, but the angle of the reflected beam isdifferent. The irradiating beam is reflected from the top surface of thesample 610 thereby generating angle “B” reflection that is directed to aposition off center on a de-scan lens 611. The de-scan lens 611 islocated at one de-scan lens focal length from the irradiation point onthe sample 610. The de-scan lens 611 then directs the angle “B”reflection to focusing lens 612. While the angle “B” reflectionirradiates the de-scan lens 611 off center, the angle “B” reflectionemitted by de-scan lens 611 is parallel to the angle “A” reflection dueto the focusing function of de-scan lens 611. Angle “B” reflectionirradiates focusing lens 612 off center as well. Focusing lens 612, byway of providing additional focusing, then directs the angle “B”reflection to a point that is centered on the detector 613. The distancebetween the point of irradiation of angle “A” reflection on the detectorand the point of irradiation of angle “B” on the detector is virtuallyzero. Therefore, using this optical system it possible to makeconsistent top surface optical measurements regardless of the angle ofthe sample being measured by the system. In this sense, the opticalsystem is independent of the angle of the sample being measured.

FIG. 33 is a diagram of an electrical system for beam tracking positionsensitive detectors. In normal operation, a sample (or wafer 714) issupported by a chuck 713 and the chuck 713 is on a Z motor (providing upand down motion) 711. The Z motor 711 is part of a feedback loop whichreceives height information from the beam tracking detector (detector521 in FIG. 30) and uses this height information to maintain the heightof the sample (by moving the Z motor up or down) via lead screw 712.This action means that the focus of the beam from the focusing lens 518is always maintained at the location of the detector 521 (as well asdetector 522). This system is implemented so that there is no focuserror at detectors 521 and 522. If the height of the sample was notmaintained at a constant position focus position errors at detectors 521and 522 would be encountered. Detector 521 is not utilized to directlymeasure the height of the sample, but rather the height of the sample isdetermined based on the distance that the Z motor has moved to keepfocus (i.e., it moves to keep the feedback error signal at a minimum).The bow or warp of the wafer is inversely proportional to the amountthat the Z stage has moved. This has the added benefit of keeping thefocus of the beam on the sample at a constant size regardless of thesample bow or warp. The micro-profiler channel (detector 522) provides ahigh frequency channel (several MHz of bandwidth). Given the highphysical movement speed required, no mechanical Z motion could everfollow this amount of bandwidth. As a result, detector 521 and thefeedback loop maintain the focus on detector 522 and the high frequencysignals received from detector 522 are direct measurements of the heightof defects or features on the sample (wafer) surface. The height is thennormalized by the reflectivity of the sample. In one example, thenormalization is performed by dividing the difference between intensitymeasurements by the sum of intensity measurements. Accordingly, detector521 is a low frequency position sensitive detection channel (operatingin the kHz range) that measures the bow or warp of a wafer by computingit from the movement of the Z motor and at the same time maintains thefocus of focusing lens 518 on the detectors 521 and 522 (therebyminimizing focus errors) while detector 522 is a high frequency (in theMHz range) position sensitive detector channel which directly measuresthe height of defects or features on the wafer surface afternormalization is applied.

FIG. 34 is a flowchart 800 of an angle independent surface heightoptical inspector. In step 801 a light beam is generated. In step 802the light beam is directed to a sample. In step 803 a reflected lightbeam that is reflected from the sample is de-scanned to generate a firstde-scanned light beam. The de-scan is performed at approximately onefocal length of a de-scan lens from an irradiation location where thelight beam irradiates the sample. In step 804 the first de-scanned lightbeam is focused to generate a focused light beam. In step 805 thelocation of the focused light beam is measured. The measuring isperformed at approximately one focal length of a focusing lens from thefocusing lens.

Although certain specific embodiments are described above forinstructional purposes, the teachings of this patent document havegeneral applicability and are not limited to the specific embodimentsdescribed above. Accordingly, various modifications, adaptations, andcombinations of various features of the described embodiments can bepracticed without departing from the scope of the invention as set forthin the claims.

What is claimed is:
 1. A method, comprising: (a) generating a lightbeam; (b) directing the light beam to a sample; (c) de-scanning areflected light beam that is reflected from the sample, therebygenerating a first de-scanned light beam; wherein the de-scanning of (c)is performed at approximately one focal length of a de-scanning lensfrom an irradiation location where the light beam irradiates the sample;(d) focusing the first de-scanned light beam, thereby generating afocused light beam; and (e) measuring the location of the focused lightbeam, wherein the measuring of (e) is performed at approximately onefocal length of a focusing lens from the focusing lens.
 2. The method ofclaim 1, wherein the generating of (a) is performed by a radiatingsource, and wherein the incident angle is within ten degrees ofBrewster's angle.
 3. The method of claim 1, wherein the directing of (b)is performed at least in part by a time-varying reflector.
 4. The methodof claim 1, wherein the de-scanning of (c) is performed by thede-scanning lens.
 5. The method of claim 1, wherein the focusing of (d)is performed by the focusing lens.
 6. The method of claim 5, wherein thefocusing lens is an achromatic lens.
 7. The method of claim 1, whereinthe measuring of (e) is performed by a detector.
 8. The method of claim7, wherein the detector is a bi-cell detector.
 9. The method of claim 7wherein the detector is a quad-cell detector.
 10. The method of claim 7,wherein the detector is a position sensitive detector.
 11. The method ofclaim 7, further comprising: (f) measuring a surface contour of thesample by measuring the height of the sample at different locationsacross the sample, wherein the measuring of (f) further includes: (f1)measuring a first location that is irradiated on the detector inresponse to irradiation at a first sample location; (f2) measuring asecond location that is irradiated on the detector in response toirradiation at a second sample location; and (f3) calculating thedifference in sample height between the first sample location and thesecond sample location based on the first location irradiated on thedetector and the second location irradiated on the detector.
 12. Themethod of claim 7, further comprising: (f) measuring a surface contourof the sample by measuring the height of the sample at differentlocations across the sample, wherein the measuring of (f) furtherincludes: (f1) measuring a first location that is irradiated on thedetector in response to irradiation at a first sample location while thesample is supported at a first support height; (f2) measuring a secondlocation that is irradiated on the detector in response to irradiationat a second sample location while the sample is supported at the firstsupport height; (f3) moving the sample to a second support height sothat the first location on the detector is irradiated in response toirradiation at the second sample location; (f4) calculating a change inheight of the sample between the first location on the sample and thesecond location on the sample based on first support height and thesecond support height.
 13. The method of claim 12, wherein the change ofheight of the sample calculated in (f4) is inversely related to thechange between the first support height and the second height.
 14. Themethod of claim 7, further comprising: (f) measuring a micro contour ofthe sample, wherein the measuring of (f) further comprises: (f1)measuring a high frequency output signal from the detector.
 15. Themethod of claim 14, wherein the high frequency output signal is abovethree-hundred kilohertz.
 16. The method of claim 15, further comprising,(f2) applying a high pass filter to the high frequency output signalfrom the detector before performing the measurement of (f1).
 17. Themethod of claim 15, wherein the detector is a bi-cell detector, andwherein a magnitude of the high frequency output signal is proportionalto a height of the sample at a current sample location.
 18. The methodof claim 15, wherein the detector is a quad-cell detector, and wherein amagnitude of the high frequency output signal is proportional to aheight of the sample at a current sample location.
 19. The method ofclaim 15, wherein the detector is a position sensitive detector, andwherein a magnitude of the high frequency output signal is proportionalto a height of the sample at a current sample location
 20. The method ofclaim 7, further comprising: (f) adjusting a sample support height thatresults in a maximum detector output frequency.
 21. The method of claim20, wherein the adjusting of (f) is performed by a processor configuredto control the height of a sample support platform.
 22. The method ofclaim 21, wherein the platform is configured to move from a lowerposition to a higher position, wherein a maximum frequency is measuredby the detector at multiple platform positions, and wherein an optimalfocus height is determined at least in part by a platform position thatresulted in the greatest maximum frequency measured by the detector.